Polyurethanes are produced by a chemical reaction between polyols and polyisocyanates, generally in the presence of auxiliary materials such as surfactants, stabilizers, blowing agents, etc., which are added to control the process and the characteristics of the resultant product, generally a foam. The polyols used in the formation of polyurethanes are compounds which contain hydroxyl groups which can react with isocyanates to form polyurethane products. There are two principal types of polyols utilized in the industry: polyester polyols and polyether polyols. The more common and most popular the the polyethers which are polymerization products of epoxides with alcohol to form ether groups (--C--O--C--) in the molecules. The polyethers synthesized in this manner may be linear, long chain polyethers which are characterized by a relatively low viscosity, or branched, short-chain polyethers which are characterized as having higher viscosities.
The polyester polyols which have been utilized in the formation of urethane polymers are obtained by the reaction of a dicarboxylic acid such as adipic acid, phthalic anhydride, dimerized linoleic acid, etc. with simple glycols and triols. The glycols used in the formation of the polyester polyols include ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, diethylene glycol, and mixtures thereof. The triols may be glycerine, 2,6-hexanetriol, trimethylolpropane and trimethylolethane.
While it is theoretically possible to produce polyurethanes from polyols and isocyanates without the use of auxiliary materials, some of the reactions take place only very slowly and often produce polyurethanes with undesirable or unusual characteristics. Industrial scale production requires the use of auxiliary materials blended in the polyol to control the progress of the reaction and to produce polyurethanes having particular properties.
Chain extenders may be included in the urethane formulations, and these components generally are glycols. Various glycols which have been used as chain extenders include ethylene glycol, diethylene glycol, 1,6-hexanediol and 1,4-butanediol. One of the difficulties including certain of the glycol chain extenders such as 1,4-butanediol is that they are incompatible with polyethers and polyesters. Accordingly, mixtures of polyethers and polyesters with 1,4-butanediol must be thoroughly homogenized prior to use.
Catalysts are used to accelerate the reaction between polyols and isocyanates. Amine and tin catalysts, and mixtures thereof have been used in urethane formulations.
In commercial production of urethanes, the procedure utilizes two liquid components which are fully compounded and delivered to the converter by the chemical manufacturer. These two components are designated in the industry as component (A), the isocyanate component and, component (B), the resin component. The resin component (B) generally contains the backbone polyol (polyether polyol or polyester polyol), chain extender, catalyst and blowing agent. Pigment and pigment dispersions also are included in or added to component (B) prior to the reaction with the polyisocyanate (component (A)). Obviously, it is desirable that the pigment or pigment dispersion be compatible with the resin component (B) so that the pigment will be uniformly dispersed in component (B). If the pigment is not compatible with component (B), then settling of the pigment and clogging of filters results.
In addition to the above materials, component (B) also may include stabilizers such as thermal and light stabilizers including ultraviolet stabilizers and antioxidants. These stabilizers also must be compatible with the materials in resin component (B).